SAPROLEGXIA IN RELATION TO THE SALMON DISEASE. 311) 



are more like eggs, or seeds, than the products of the zoo- 

 sporangia or those of the dictyosporangia. 



The summit of a hypha, or a short branch of a hyplia, 

 dihites into a spheroidal sac, the cellulose wall of which 

 becomes thickened, but presents, here and there, thin places, 

 looking like clear circular dots, or apertures, under the 

 microscope. Protoplasm accumulates in the spheroidal case 

 thus formed; and either remains a single rounded mass, or 

 divides into a smaller or greater number of spheroids, each 

 of which, much larger than a single zoospore, is an Oospore. 

 The oospore, or oospores, thus formed eventually become 

 invested by a thick cellulose coat. Before this happens, iu 

 some forms of Saprolegnia, slender twig-like branches are 

 given off either from the stalk of the oosporangium or from 

 an adjacent hypha, and the terminal portion of one or more of 

 these twigs applies itself to the oosporangium. This terminal 

 portion becomes shut off from the rest of the twig by a trans- 

 verse septum, and is an Antheridium. The antheridiura 

 pierces the wall of the oosporangium, divides into as many 

 branchlets as there are oospores, and one branchlet applies 

 itself to each oospore. In all probability something passes 

 from the antheridium into the oospore, and effects fecunda- 

 tion (Fig. V, p. 316). 



Thus the oosporangium represents a female reproductive 

 organ, and the oospore takes the place of an e^^, or an 

 embryo cell. The antheridium represents a male organ, and 

 its contents represent the essential substance of spermato- 

 zuids, or the fertilising matter of a pollen tube ; and, after 

 fecundation, the oospores answer to impregnated ova or 

 fertilised seeds. 



The oosporangium may burst and give exit to the oospores, 

 or it may fall with them to the bottom. And, as a general 

 rule, the oospores remain for a long time, sometimes several 

 months, unchanged. Sooner or later, however, they 

 germinate J and this process may take place in various 

 ways : 



1. The contents of the oospore may divide directly into 

 locomotive zoospores which are set free. 



2. The oospore may send out a hypha, the apical part of 

 which becomes converted into a zoosporangium. 



y rpi to 



6. ihe oospore may send out a hypha, and this coming 

 into contact with the body of a fly or some such matter, may 

 develop into a mycelium iu the ordinary way. 



The whole series of phenomena now described represents 

 the fullest set of changes known to occur in any one form 

 of Saprolegnia, But, even in the same form, the series 



VOL. XXII. NEW SEU. X 



